A PET scanner, or Positron Emission Tomography scanner, is a medical imaging device that helps doctors see how organs and tissues are functioning in the body. It works by using a small amount of radioactive material, which is injected into the patient. This material emits positrons, which are detected by the scanner to create detailed images of metabolic activity. PET scans are often used in oncology to detect cancer, assess its spread, and monitor treatment effectiveness. They can also help evaluate brain disorders, heart conditions, and other diseases by providing insights into how well different parts of the body are working.